#include <iostream>
using namespace std;
int main(){
	int cycleNumber;
	int sum = 0;
	int i = 0;
	
	cin >> cycleNumber;
	do{
		sum += i;
		i++;
	}while(i <= cycleNumber);
	
	cout << "The resulf of sum:" << sum << endl;
	
	return 0;
}
